Developing apparatus used in electrophotography

ABSTRACT

Developing apparatus includes two endless bands each of which is horizontally disposed, carries a plurality of horizontally spaced magnets depending therefrom and traverses the path of a photoconductive sheet having a latent image thereon whereby to brush said sheet with an excess of developer carried by a first of said belt and magnets and subsequently to brush the developed sheet with magnetic carrier particles carried by the other of said belts and magnets thereon to thereby remove excess toner.

[ 51 Apr. 9, 1974 United States Patent 1191 Saito et al.

FOREIGN PATENTS OR APPLICATIONS 959 959 Olden l MG... e kk r mmq CLH 957 067 9999 /I,/HH 26 957 360945 6 41 .287 .2 42 32 79 nU 9 222334 0, Japan !'29,544 0/0000 Canada ll8/637 22 Filed: Apr. 23, 1973 Appl. No; 353,679

Primary Examiner-Morris Kaplan Robert E. Burns; Emman- Related [15. Application Data Attorney, Agent, or Firm uel J. Lobato [60] Division of Ser, No. 139,!39, April 30, I971,

abandoned. which is a continuation of Ser. 772,752, Nov 1. 1968,3bandoned.

[57] ABSTRACT Developing apparatus includes two endless bands each of which is horizontally disposed,

carries a plurality of Ms we 1, 0 7 2 I0 9 it 36 m 8 mm 1H8 7 m. 3 H 6 u 1 8 um I n I mrm Hr. mm m L TI C .M .w U'mF H N 555 horizontally spaced magnets depending therefrom and traverses the path of a photoconductive sheet having a References Cited latent image thereon whereby to brush said sheet with UNITED STATES PATENTS an excess of developer carried by a first of said belt and magnets and subsequently to brush the developed sheet with magnetic carrier particles carried by the other of said belts and magnets thereon to thereby remove excess toner.

ll7/i7.5 X

XX 57 3 o 1 ll 209/218 x Reuter, .lr.

7 Claims, 3 Drawing Figures DEVELOPING APPARATUS USED IN ELECTROPHOTOGRAPHY This is a division of appiication Ser. No. l39,l39, filed Apr. 30, 1971, now abandoned, which was a continuation of application Ser. No. 772,752, filed Nov. l, 1968, now abandoned.

The present invention relates to an improved developing apparatus used in electrophotography, more particularly relates to an improved developing apparatus of a magnet-brush type used in electrophotography including a first developing stage and a second developing stage arranged in sequence in the advancing path of a photoconductive sheet.

An electrophotography process employs a developing process to develop a latent electrostatic image formed on the electroconductive sheet into a visible image using a developer containing toners and carriers. One of the methods which can be used advantageously for developing the visible image on the sheet is the socalled magnet-brush type method, wherein a magnet carries, as a developer, toners composed of numerous extremely small particles of colored thermosoluble plastic resin and carriers composed of magnetized iron powder. However, it is difficult to control the content of the toner in the developer in case of the conventional magnet-brush type developing process. A large excess of the toner in the developer causes extraordinary depositing of the toner on the latent image on the sheet resulting in an obscure visible image and further causes unfavourable depositing of toner on the portion of the sheet adjacent to the latent image resulting in the production of the so-called shades around the visible image which is finaily acquired on the photoconductive sheet. Therefore, it is a fundamental requirement to limit the content of the toner in the developer within an optimum range in order to acquire a fine visible image on the sheet by the magnet-type developing method.

However, in case a large number of photoconductive sheets are advanced in succession through the magnettype developing apparatus in an actual electrophotography process, the carrier carried by the magnet is not consumed throughout the process while the toner carried by the magnet is gradually consumed because the carrier is successively transferred from the magnet to the latent image formed on the sheet. It is therefore difficult to keep the content of the toner particles within the developer constant within an optimum working range.

A principal object of the present invention is to provide an improved developing apparatus of the magnetbrush type used in electrophotography which can provide a fine visible image on a photoconductive sheet without production of shades.

Another object of the present invention is to provide an improved developing apparatus of the magnet-brush type used in electrophotography in which difficulty in the supply of the toner, which was usually the case with the conventional developing apparatus of magnetbrush type, is eliminated.

A further object of the present invention is to provide an improved developing apparatus of the magnetbrush type used in electrophotography which can comply with the requirement for an extremely fine visible image on a photoconductive sheet necessary when using the sheet acquired as a negative in offset printing.

A still further object of the present invention is to provide an improved developing apparatus of the magnet-brush type used in electrophotography which can be used for processing a large number of sheets in succession in a constant condition.

Making the image acquired on the sheet finer by cleaning the surface of the sheet prior to the fixing operation by using a magnetic cleaning brush carrying only the carrier is a well-known art. In this manner, the toner deposited on the image in excess or deposited on the portions of the sheet adjacent to the image is eliminated by the magnetic cleaning brush. As a result of repeated experiments by the inventors of the present invention, it was confirmed that a cleaning effect on the surface of the sheet is obtained by slightly brushing the surface with the aforementioned magnetic cleaning brush immediately after the development of the image whereby the toner deposited on the portion of the surface adjacent to the image during developing is eliminated and no shade remains on the surface. Further, it was also confirmed that a fading-out effect on the visibie image is obtained by the application of the aforementioned magnetic cleaning brush, that is, only a necessary but sufficient quantity of the toner is left on the image and the excess toner bestowed by development is eliminated.

From the results of the aforementioned experiment, the inventors of the present invention have found that a constant developing effect can be obtained by empioying two developing stages, that is a first developing stage carried out by using a developer with a high toner content and a second developing stage carried out by using a magnetic cleaning brush.

In accordance with the aforementioned objects and discussions, the developing apparatus of the present invention comprises two developing stages arranged in sequence along the path of a photoconductive sheet advanced through the apparatus. The first developing stage includes a developing device of the ordinary type with the only exception that a developer with a high toner content is used for a magnet brush. As a result of this high content ratio of the toner within the developer, an excessive quantity of the toner particles is deposited upon the image in this stage resulting in overdevelopment of the image and the production of shades surrounding the image. In order to eliminate the excessively deposited toner particles, the second developing stage of the apparatus of the present invention includes a developing apparatus of the ordinary type with the only exception that a magnetic cleaning brush carrying only the carrier is used as the magnet brush. By the application of the magnetic cleaning brush, only the excessively deposited toner particles on the image are eliminated and the so-called fading-out effect on the visible image is acquired, while the toner particles deposited on the portion of the surface adjacent to the image are also cleaned up and shaded areas surrounding the image can be eliminated.

The aforementioned combination of the excessive supply of the toner particle causing over-development in the first developing stage and the fading-out effect by the second developing stage assures a finer visible image on the photoconductive sheet finally acquired than that obtained by the ordinary single stage developing method using a developer including an adequate quantity of toner. This is because of the fact that the high fidelity of the developed image to the master image is assured by the excessive developing during the first developing stage and that cleaning of the visible image obtained is assured by the fading-out effect by the second developing stage. Therefore, the electrophotograph made by the apparatus of the present invention can advantageously be adopted to offset printing techniques wherein the photoconductive sheet obtained by electrophotography process is used as a negative in printing.

As mentioned above, the developer used in the first developing stage of the present invention contains a toner content considerably higher than that of the toner content used in the ordinary optimum developing process. Because of such a considerably high toner content, a large number of photoconductive sheets can be processed in succession through the apparatus of the present invention with a constant developing effect and without supplementing the toner. In other words, replacement of the spent developer or replenishment of toner to the old developer is required only after processing thousands of photoconductive sheets.

With respect to the magnetic cleaning brush of the second development stage, the tone particles on the photoconductive sheet are transferred sheet by sheet to the cleaning brush and are gradually accumulated thereon. Consequently, the cleaning brush carries not only the carrier but also the toner after processing thousands of sheets. It will therefore be necessary to replace the old carrier with a new one only after processing thousand of sheets.

Further features and advantages ofthe present invention will be apparent from the ensuing description, reference being made to the accompanying drawings wherein:

FIG. 1 is a perspective view of one embodiment of the developing apparatus of the present invention,

FIGS. 2 and 3 are, respectively, a perspective view and a side view of another embodiment of the developing apparatus of the present invention.

Referring to FIG. 1, an embodiment of the developing apparatus of the present invention is shown. The embodiment comprises two developing stages 1 and 2 arranged in sequence along the path of travel of a photoconductive sheet containing thereon an electrostatic image 3 processed in the apparatus. The first developing stage effects over-development of the image and comprises a pair of sprockets 4a and 4b and a circulating chain 5 meshing with the sprockets 4a and 4b. Each of the sprockets 4a and 4b is mounted firmly on shafts 6a and 612, respectively, and one of the shafts 6a and 6b is connected to a given driving source (not shown). The chain 5 is arranged in such a manner that the path or course of the chain 5 transverses the path of the photoconductive sheet 3 at approximately a right angle. The chain 5 is provided with a plurality of spaced-apart magnets 7 disposed relative to each of the links 8 composing the chain 5 in such a manner that the magnets form a ring formation with each of the magnets facing the photoconductive surface of the photoconductive sheet 3. Each of the magnets 7 carries a developer 9 composed of a mixture of toner particles and carrier powder. The content of the toner with respect to the amount of the carrier is in the range of from 5% to 50% and preferably 23% by weight.

The second developing stage 2 is positioned downstream of the first developing stage 1 and compensates for the excessive over-development of the image caused by the first stage 1. The second developing stage 2 comprises a pair of sprockets 14a and 14b and a circulating chain 15 meshing with the sprockets 14a and 14b. Each of the sprockets 14a and 14b is mounted firmly on shafts 16a and 16b, respectively, and one of the shafts 16a and 16b is connected to a given driving source (not shown). The circulation of the chain l5 may be either synchronized with that of the chain 5 or independent of that of the chain 5 according to the requirement of the actual developing process. The chain 15 is arranged in a manner similar to that of the chain 5 of the first developing stage 1 with respect to the path of the photoconductive sheet 3. The chain 15 is provided with a plurality of spaced-apart magnets 17 disposed relative to each of the links 18 composing the chain 15 in a manner similar to the magnets 7 of the chain 5 of the first developing stage 1. Each magnet 17 carries only carrier powder 19.

The photoconductive sheet 3 is supported on a supporting plate 21 which travels along a guide member 22 from an inlet to an outlet of the apparatus at a given traveling speed. The traveling of the supporting plate 21 is actuated by a suitable driving source (not shown). However, in case a number of photoconductive sheets are to be processed successively through the apparatus, such mechanism as a conveyer can also be adopted instead of the supporting plate for carrying the sheets.

In the aforementioned mechanical arrangement of the developing apparatus, the photoconductive sheet 3 is advanced in the direction shown with the arrow 23, dusted with an excess quantity of the toner particles applied by the magnets 7 circulating or advancing with the chain 5 while passing through the first developing stage 1 and cleaned by magnetically removing excess developer by the cleaning magnet 17 circulating or advancing with the chain 15 while passing through the second developing stage 2. Thus a remarkably fine visible image is obtained on the photoconductive sheet 3 coming out of the outlet of the developing apparatus.

Referring to FIGS. 2 and 3, another embodiment of the developing apparatus of the present invention is shown. In this embodiment, the photoconductive sheet 3 is wound on a cylinder rotatable 31 rotating in the direction shown with the arrow 32. A magnet rod 33 extending over at least the width of the sheet forms the first developing stage and carries the developer, the same as that of the foregoing embodiment while a magnet rod 34 extending over at least the width of the sheet at a position downstream of the magnet rod 33 forms the second developing stage and carries only the carrier. With the rotation of the cylinder 31 carrying the photoconductive sheet, the sheet is dusted excessively with the toner particles in the first developing stage and cleaned in the second developing stage. Thus a considerably fine visible image is acquired on the photoconductive sheet.

While the invention has been described in conjunction with certain embodiments thereof, various changes and modifications may be made without departing from the scope and spirit of the present invention.

What is claimed is:

1. An improved developing apparatus used in electrophotography comprising means for advancing a photoconductive sheet provided with a latent image formed thereon through said apparatus; and two developing stages arranged in sequence along the path of said advanced photoconductive sheet, the first one of said developing stage including a developing device carrying a developer containing an excess quantity of toner particles and comprising a pair of sprockets firmly mounted on respective shafts, a driving source connected to one of said shafts, and a circulating chain meshing with said sprockets, a circulating path of said chain traversing said path of said advancing photoconductive sheet at approximately a right angle and said chain being provided with a plurality of magnets carrying said developer and connected to links composing said chain such that they face the photoconductive surface of said photoconductive sheet; and the second one of said developing stage including a cleaning device carrying only carrier powder and comprising a pair of sprockets firmly mounted on respective shafts, a driving source connected to one of said shafts, and a circulating chain meshing with said sprockets, a circulating path of said chain traversing said path of said advancing photoconductive sheet at approximately a right angle and said chain being provided with a plurality of magnets carrying said powder and connected to links composing said chain such that they face said photoconductive surface of said photoconductive sheet; whereby said photoconductive sheet is excessively dusted with said toner particles while passing through said first developing stage and subsequently cleaned while passing through said second developing stage.

2. An apparatus according to claim 1; wherein said means for over-developing the latent electrostatic image includes a source of developer composed of a mixture of toner and magnetic carrier particles in sufficient quantities with respect to each other to effect excessive development of the image.

3. An apparatus according to claim 2; wherein the quantity of said toner particles with respect to said magnetic carrier particles is approximately 23% by weight.

4. An apparatus for developing in two stages a latent electrostatic image carried on a photoconductive sheet comprising: advancing means for advancing a photoconductive sheet having thereon a latent electrostatic image along a given path of travel; first-stage developing means for over-developing the latent image during advancement thereof along said path of travel, said first-stage developing means comprising a source of developer composed of a mixture of toner particles and magnetic carrier particles in sufficient relative quantities to effect excessive over-development of the latent image, a first plurality of magnets interconnected in spaced-apart relationship in a first ring formation, and means for driving said first ring formation of magnets around a first endless course having a portion thereof extending adjacent said source of developer to enable said magnets to attract therefrom said mixture and having another portion thereof extending transversely across said path of travel in sufficient proximity to the photoconductive sheet to enable said magnets to deposit thereon an excessive quantity of toner particles in sufiicient excess of the amount required to develop the latent image to thereby effect excessive overdevelopment of the latent image and shading of the area surrounding the image; and second-stage developing means extending across said path of travel downstream from said first-stage developing means for compensating for the over-development of the latent image by removing sufficient excess toner particles from the photoconductive sheet to effect partial fading-out of the excessively developed image and elimination of the shading surrounding the image to thereby produce a high fidelity visible image, said second-stage developing means comprising a second plurality of magnets interconnected in spaced-apart relationship in a second ring formation; said second plurality of magnets each carrying magnetic carrier particles only; and means for driving said second ring formation of magnets around a second endless course having a portion thereof extending transversely across said path of travel in sufficient proximity to the photoconductive sheet so that said magnets and carrier particles attract therefrom said sufficient excess of said toner particles.

5. An apparatus according to claim 4 wherein said first-stage developing means includes a first endless chain having said first plurality of magnets connected thereto to define said first ring formation, and wherein said means for driving said first ring formation includes a set of rotatable sprocket wheels in engagement with said first endless chain; wherein said second-stage developing means includes a second endless chain having said second plurality of magnets connected thereto to define said ring formation, and wherein said means for driving said second ring formation includes another set of rotatable sprocket wheels in engagement with said second endless chain.

6. An apparatus according to claim 4 wherein the quantity of said toner particles with respect to said magnetic carrier particles is in the range of from 5% to 50% by weight.

7. An apparatus according to claim 4 wherein the quantity of said toner particles with respect to said magnetic carrier particles is approximately 23% by weight.

a t m =0 UNITED STATES PATENT OFFICE 6 CERTIFICATE OF CORRECTION Patent 3. 802.389 Dated April 9 1974 Inventor( Akira SAITO and Yukihisa SHIBASAKI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: In the heading of the patent, Item {76] after "Iwasaki" insert --Tsushinki- Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Arresting Officer Commissioner of Patents 'ORM PC4050 "0-69) USCOMM-DC ooa're-Puo 

1. An improved developing apparatus used in electrophotography comprising means for advancing a photoconductive sheet provided with a latent image formed thereon through said apparatus; and two developing stages arranged in sequence along the path of said advanced photoconductive sheet, the first one of said developing stage including a developing device carrying a developer containing an excess quantity of toner particles and comprising a pair of sprockets firmly mounted on respective shafts, a driving source connected to one of said shafts, and a circulating chain meshing with said sprockets, a circulating path of said chain traversing said path of said advancing photoconductive sheet at approximately a right angle and said chain being provided with a plurality of magnets carrying said developer and connected to links composing said chain such that they face the photoconductive surface of said photoconductive sheet; and the second one of said developing stAge including a cleaning device carrying only carrier powder and comprising a pair of sprockets firmly mounted on respective shafts, a driving source connected to one of said shafts, and a circulating chain meshing with said sprockets, a circulating path of said chain traversing said path of said advancing photoconductive sheet at approximately a right angle and said chain being provided with a plurality of magnets carrying said powder and connected to links composing said chain such that they face said photoconductive surface of said photoconductive sheet; whereby said photoconductive sheet is excessively dusted with said toner particles while passing through said first developing stage and subsequently cleaned while passing through said second developing stage.
 2. An apparatus according to claim 1; wherein said means for over-developing the latent electrostatic image includes a source of developer composed of a mixture of toner and magnetic carrier particles in sufficient quantities with respect to each other to effect excessive development of the image.
 3. An apparatus according to claim 2; wherein the quantity of said toner particles with respect to said magnetic carrier particles is approximately 23% by weight.
 4. An apparatus for developing in two stages a latent electrostatic image carried on a photoconductive sheet comprising: advancing means for advancing a photoconductive sheet having thereon a latent electrostatic image along a given path of travel; first-stage developing means for over-developing the latent image during advancement thereof along said path of travel, said first-stage developing means comprising a source of developer composed of a mixture of toner particles and magnetic carrier particles in sufficient relative quantities to effect excessive over-development of the latent image, a first plurality of magnets interconnected in spaced-apart relationship in a first ring formation, and means for driving said first ring formation of magnets around a first endless course having a portion thereof extending adjacent said source of developer to enable said magnets to attract therefrom said mixture and having another portion thereof extending transversely across said path of travel in sufficient proximity to the photoconductive sheet to enable said magnets to deposit thereon an excessive quantity of toner particles in sufficient excess of the amount required to develop the latent image to thereby effect excessive over-development of the latent image and shading of the area surrounding the image; and second-stage developing means extending across said path of travel downstream from said first-stage developing means for compensating for the over-development of the latent image by removing sufficient excess toner particles from the photoconductive sheet to effect partial fading-out of the excessively developed image and elimination of the shading surrounding the image to thereby produce a high fidelity visible image, said second-stage developing means comprising a second plurality of magnets interconnected in spaced-apart relationship in a second ring formation; said second plurality of magnets each carrying magnetic carrier particles only; and means for driving said second ring formation of magnets around a second endless course having a portion thereof extending transversely across said path of travel in sufficient proximity to the photoconductive sheet so that said magnets and carrier particles attract therefrom said sufficient excess of said toner particles.
 5. An apparatus according to claim 4; wherein said first-stage developing means includes a first endless chain having said first plurality of magnets connected thereto to define said first ring formation, and wherein said means for driving said first ring formation includes a set of rotatable sprocket wheels in engagement with said first endless chain; wherein said second-stage developing means includes a second endless chain having said second plurality of magnets connected therEto to define said ring formation, and wherein said means for driving said second ring formation includes another set of rotatable sprocket wheels in engagement with said second endless chain.
 6. An apparatus according to claim 4; wherein the quantity of said toner particles with respect to said magnetic carrier particles is in the range of from 5% to 50% by weight.
 7. An apparatus according to claim 4; wherein the quantity of said toner particles with respect to said magnetic carrier particles is approximately 23% by weight. 